Recently, several laboratories have obtained evidence that changes in ion fluxes may act as signals for differentiation and growth regulation in eukaryotic cells. We wish to increase our knowledge of the molecular basis of cellular differentiation using a murine pre-B cell tumor system as a model. The specific aim of this proposal is to test the hypothesis that lipopolysaccharide (LPS)-induced differentiation of a clonal pre-B cell line is mediated by a transitory rise in cytoplasmic Na+ levels. In particular, we wish to understand the molecular mechanisms by which LPS induces an increase in cellular Na+ and what subsequent events are critical for signalling expression of surface immunoglobulin. It is suggested that there is an increase in Ca++ flux induced by the rise in Na+. Another aim of this proposal is to test the hypothesis that this change in cellular Ca++ serves as a trigger for later events in differentiation such as nRNA transcription and processing, and new protein synthesis. These processes could be regulated by changes in enzyme/protein phosphorylation mediated by Ca++ requiring protein kinases. These questions will be examined by determining the effects of LPS on Na+ and Ca++ fluxes in 70Z/3 cells using isotopic tracer techniques. This project will also study the roles of membrane ion channels such as the Na+/Ca++ and the Na+/H+ antiporters using specific inhibitors of these pathways. We will also examine the Ca++ (and perhaps Na+)-dependent regulation of several key protein/enzyme systems such as the phosphorylation of the S6 ribosomal protein during LPS-induced differentiation in 70Z/3 cells.